Keyboards are used in a variety of different portable and stationary applications, such as palmtop or hand-held computers, notebook computers, sub-notebook computers, digital organizers or personal digital assistants (PDAs), digital cameras with annotation or editing capability, data-capable mobile phones, video consumer game electronics, entertainment electronics, calculators, stationary telephones, and small form-factor stationary (desktop) computers, to enter text, numerical, and/or control information. In many of these portable and stationary applications, it is desirable for the overall size of the keyboards to be reduced when the keyboards and products are stored and transported, especially for portable applications. However, during use, it is desirable for the keyboards to conform to standard sizes to have a typical "feel" for ease and comfort of use. The overall size of the keyboard is particularly critical for text entry via "touch typing." As discussed below, a variety of different types of keyboards have been developed to meet these contradictory requirements with varying degrees of success.
One solution to achieve both small overall size during storage and transport and standard size during use is the "fixed segment", i.e. no sliding segments, folding keyboard design. Characteristic of these designs is that the keyboard is divided into segments which fold, but do not slide and with the keys maintaining a fixed position on the segment. They are then hinged in a manner that permits the keys to properly align when the keyboard is in the open position. Examples of this design are set forth in U.S. Pat. No. 3,940,758 to Margolin, U.S. Pat. No. 5,187,644 to Crisan, U.S. Pat. No. 5,278,779 to Conway et al., U.S. Pat. No. 5,457,453 to Chiu et al., U.S. Pat. No. 5,519,569 to Sellers, U.S. Design Pat. No. 254,554 to Genaro et al., U.S. Design Pat. No. 299,030 to Menn, U.S. Design Pat. No. 322,246 to Izaki, and U.S. Design Pat. No. 324,035 to Izaki which are all herein incorporated by reference.
One of the problems with this prior design is with the electrical interconnections between the central segment and the folding segment which arise from two issues. First, because the layout of a standard typing keyboard offsets the rows of keys, the ends of the keyboard segments present a "stepped" pattern. This complicates and limits the available methods of electrical interconnection between the segments and makes it very difficult to provide Electro Static Discharge (ESD) protection at the points of interconnection when the keyboard is in the folded state. The "stepped" pattern when the keyboard is in the folded state presents mechanical problems with providing a mechanically and aesthetically suitable protective cover, often dictating a complicated cover with multiple hinged segments to protect the exposed edges from ESD, environmental and impact damage. Second, the pivoting nature of the folding segment with respect to the central segment brings the one set of the interconnecting mating electrical connectors in towards the other set of connectors at an arc, rather than straight on, which imposes limitations on the interconnection methods. Typically, the electrical interconnection is made either by a flexible ribbon type connector or by interconnecting mating electrical connectors along the side of each segment which are joined together. Unfortunately, the flexible ribbon type connectors are subject to fatigue over time from the bending and can fray and break. Due to the arc-shaped path followed by the opening keyboard segment when opened, it is impossible to use an interconnection method that relies on mating connecting members approaching along a straight-line path, or upon continuous, uniform compression from the top to the bottom of the connecting region.
Another problem with this design is that when the folding segments are folded out from the central segment they are not securely held in place. As a result, the resulting expanded or full size keyboard is flimsy unless an additional locking mechanism is provided.
Another design to achieve both small overall size during storage and transport and standard size during use is disclosed in U.S. Pat. No. 5,267,127 to Pollitt which is herein incorporated by reference. In this design, the keyboard assembly is split in half and each half of the keyboard assembly can be slid along a keyboard axis between a split position and a connected position. The halves of the keyboard assembly are not folded with respect to each other.
One of the problems with this design is that the width or depth of the electronic product on which the halves of the keyboard assembly ride on and are stored on is still fairly large. It is a property of this design that the degree of expansion in the overall length of the keyboard is in proportion to the depth of the unit. As a result, overall size is not significantly reduced. Additionally, because the size is not significantly reduced, this design is not desirable for some smaller applications, such as handheld computers or mobile telephones.